In a visor of this kind, known from German Design Pat. No. 75 29 457, the transparent panel is held in a nonreleasable manner in a frame. In order to impart the required stability to the transparent panel, the panel is adapted to the curvature of the frame, which is dictated by the external shape of the protective helmet.
Transparent panels of this kind may be made of hard, scratch-resistant mineral glass, as in the case of German Design Pat. No. 75 29 457, or--as is much more widespread in practice--of a transparent plastic. Plastic, however, is far less scratch-resistant than mineral glass.
It is further known, for instance from German Design Pat. No. 78 10 225, to embody a visor panel entirely of a plastic that is as scratch-resistant as possible and is screwed directly onto the protective helmet. Visor panels of this kind, which are not received in frames, must from the outset have a curvature corresponding to the external contour of the protective helmet in the vicinity of its view opening; that is, they must be produced by injection molding and are necessarily relatively thick.
It is common to all these embodiments that the transparent panel can be replaced only with the exertion of some effort, and that in particular the transprent panel itself is relatively expensive in terms of effort and accordingly of cost. It is impossible to make a rapid change during a brief pause while driving in order to exchange a dirty transparent panel for a clean one.